Support setting target_sdk_version separately from sdk_version

Before this change, if targetSdkVersion wasn't set in the
AndroidManifest.xml, we'd set it to the sdk_version from the Android.bp.

But there are cases where you want to compile against a later SDK, but
target an earlier one (especially if you depend on libraries that need
to be compiled against more recent SDKs, like androidx).

Test: build APK with different target_sdk_version.
Change-Id: Iaed36b522955a374a049ef331158cc8fc5798ad2

java/aar.go

@@ -413,6 +413,10 @@ func (a *AARImport) minSdkVersion() string {
 	return a.sdkVersion()
 }
 
+func (a *AARImport) targetSdkVersion() string {
+	return a.sdkVersion()
+}
+
 var _ AndroidLibraryDependency = (*AARImport)(nil)
 
 func (a *AARImport) ExportPackage() android.Path {

java/android_manifest.go

@@ -58,7 +58,7 @@ func manifestMerger(ctx android.ModuleContext, manifest android.Path, sdkContext
 		Output: fixedManifest,
 		Args: map[string]string{
 			"minSdkVersion":    sdkVersionOrDefault(ctx, sdkContext.minSdkVersion()),
-			"targetSdkVersion": sdkVersionOrDefault(ctx, sdkContext.sdkVersion()),
+			"targetSdkVersion": sdkVersionOrDefault(ctx, sdkContext.targetSdkVersion()),
 			"args":             strings.Join(args, " "),
 		},
 	})

java/droiddoc.go

@@ -484,6 +484,10 @@ func (j *Javadoc) minSdkVersion() string {
 	return j.sdkVersion()
 }
 
+func (j *Javadoc) targetSdkVersion() string {
+	return j.sdkVersion()
+}
+
 func (j *Javadoc) addDeps(ctx android.BottomUpMutatorContext) {
 	if ctx.Device() {
 		if !Bool(j.properties.No_standard_libs) {

java/java.go

@@ -183,6 +183,10 @@ type CompilerDeviceProperties struct {
 	// Defaults to sdk_version if not set.
 	Min_sdk_version *string
 
+	// if not blank, set the targetSdkVersion in the AndroidManifest.xml.
+	// Defaults to sdk_version if not set.
+	Target_sdk_version *string
+
 	// if true, compile against the platform APIs instead of an SDK.
 	Platform_apis *bool
 
@@ -425,11 +429,20 @@ func (j *Module) minSdkVersion() string {
 	return j.sdkVersion()
 }
 
+func (j *Module) targetSdkVersion() string {
+	if j.deviceProperties.Target_sdk_version != nil {
+		return *j.deviceProperties.Target_sdk_version
+	}
+	return j.sdkVersion()
+}
+
 type sdkContext interface {
 	// sdkVersion eturns the sdk_version property of the current module, or an empty string if it is not set.
 	sdkVersion() string
 	// minSdkVersion returns the min_sdk_version property of the current module, or sdkVersion() if it is not set.
 	minSdkVersion() string
+	// targetSdkVersion returns the target_sdk_version property of the current module, or sdkVersion() if it is not set.
+	targetSdkVersion() string
 }
 
 func sdkVersionOrDefault(ctx android.BaseContext, v string) string {